<!--------------------general ajax function------------------------------------!>
//start ajax code.
function GetXmlHttpObject(handler)
{   var objXMLHttp=null
	 if (window.XMLHttpRequest)
	 {
		objXMLHttp=new XMLHttpRequest();
	 }
	 else if (window.ActiveXObject)
	 {
		objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP");
	}
	 return objXMLHttp;
}
<!--------------------for user auctantication------------------------------------!>
function stateChanged_user()
{
	if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
	{
		document.getElementById("show_user_available").innerHTML=xmlHttp.responseText;
	}
}

function check_user_available(path,user)
{
	xmlHttp=GetXmlHttpObject();
	if (xmlHttp == null)
	{
		alert ("Browser does not support HTTP Request");
		return;
	}
	var url=path+"common/forgot_password_available.php"
	url=url+"?user_name="+user
	url=url+"&sid="+Math.random();
	xmlHttp.onreadystatechange=stateChanged_user; 
	xmlHttp.open("GET",url,true) ;
	xmlHttp.send(null);
}

<!--------------------for email auctantication------------------------------------!>
function stateChanged_email()
{
	if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
	{
		document.getElementById("show_email_available").innerHTML=xmlHttp.responseText;
	}
}

function check_email_available(path,email)
{
	xmlHttp=GetXmlHttpObject();
	if (xmlHttp == null)
	{
		alert ("Browser does not support HTTP Request");
		return;
	}
	var url=path+"common/forgot_password_available.php"
	url=url+"?email="+email
	url=url+"&sid="+Math.random();
	xmlHttp.onreadystatechange=stateChanged_email; 
	xmlHttp.open("GET",url,true) ;
	xmlHttp.send(null);
}